This invention relates to electric lamps and, in particular, to an improved lead wire for incandescent lamps.
In the prior art, various materials have been used for lead wire in electric lamps. A recurring problem has been the weakening or annealing of the lead wire during glass forming operations. As a specific example, in making incandescent lamps, the lead wires and exhaust tube are inserted into a flare and the smaller end of the flare is heated and pressed to make what is known as the stem.
The stem press operation softens the lead wires to the point that tie wires are used to assure lamp reliability, particularly against shock. The button forming and tie wire operations add steps to the manufacture of lamps, increasing cost and adding a possible source of shrinkage (rejected lamps). Alternatively, simply removing the tie wires may result in premature failure of the lamp in use. Specifically, the heat from the filament anneals the leads somewhat reducing the stiffness thereof. Subsequent shock may deform the lead wires such that the filament is spatially deformed, which can lead to immediate or premature filament failure.